A storing unit stores, amongst coefficients, values of a coefficient group associated with one selected from multiple variable groups, which are obtained by dividing state variables of an evaluation function. A searching unit searches for a solution to an optimization problem by repeating update processing, which includes calculating, using the values of the coefficient group, a value change of the evaluation function responsive to changing the value of each state variable of the variable group and changing the value of one state variable thereof based on the value change and temperature. A processing unit calculates multiplicity indicating the iteration count in which the values of the variable group are maintained in a search using Markov chain Monte Carlo (MCMC), and causes, responsive to cumulated multiplicity exceeding a threshold, the searching unit to perform the update processing using the values of the coefficient group associated with a different variable group.